Color signal processing circuit with residual phase error correction

ABSTRACT

A color signal processing circuit which includes a conversion unit for converting two color difference signals, which are equivalent to color difference signals obtained by color demodulation of a color signal by using two color difference axes intersecting perpendicularly to each other. The color difference signals are converted into a color amplitude signal corresponding to the amplitude of the color signal and a color phase signal corresponding to the phase of the color signal. Also included is a signal processing unit for processing at least either of the color amplitude signal and the color phase signal. Thus, it is easy to obtain a color difference signal in which a residual phase error included in the color signal is eliminated.

This application is a division of application Ser. No. 07/514,487 filedApr. 25, 1990.

BACKGROUND OF THE INVENTION

1. Field of The Invention

This invention generally relates to a color signal processing circuit(hereunder sometimes referred to as a color signal circuit). Moreparticularly, this invention relates to a color signal circuit, whichcan be applied to various equipment, having an automatic phase control(APC) circuit provided in a portion for generating a carrier to be usedin a frequency conversion and color demodulation operations of a carrierchrominance signal, to a color signal circuit having an automatic colorcontrol function and to a hue control circuit for controlling a hue of acolor indicated by a color difference signal.

2. Description of The Related Art

There has been a color signal circuit for use in various equipment suchas a color television receiver and a color video tape recorder (VTR)which is provided with an APC circuit in a portion for generating acarrier to be used in the signal processing thereof.

FIG. 10 is a schematic block diagram for showing the construction of anexample of a conventional APC circuit provided in the playback system ofa color VTR which is adapted to shift the phase of a low frequency bandcarrier chrominance signal by 90 degrees every horizontal scanningperiod (hereunder sometimes referred to simply as 1-H period) andreverse the direction of the phase shift of the low frequency bandcarrier chrominance signal at every sequential video track and recordand playback a signal obtained by the frequency division multiplexing ofthe low frequency band carrier chrominance signal and a low frequencyband modulated luminance signal.

In the conventional APC circuit of FIG. 10, reference numeral 1 denotesan input terminal for receiving a reproduced color signal (that is, areproduced low frequency band carrier chrominance signal); 2 anautomatic chroma control circuit (hereunder referred to as a colorcontrol (ACC) circuit) for automatically adjusting the signal level of acolor signal to a predetermined value; 3 and 9 frequency conversioncircuits; 4 and 10 band-pass filters (hereunder sometimes abbreviated asBPFs); 5 (1/2)-burst circuit; 6 a 1-H delay line; 7 a color killercircuit; 8 an automatic frequency control (AFC) circuit; 11 a variablecrystal oscillator (VCO); 12 a reference crystal oscillator; 13 and 16phase comparison circuits; 14 a burst gate circuit; 15 a color killerdetection circuit; 17 a phase shifting circuit (hereunder sometimesreferred to as a phase shifter) for shifting the phase of an inputsignal thereto by 90 degrees; and 18 an adder. Incidentally, a referencechrominance subcarrier is supplied from the crystal oscillating circuit12 to the phase comparison circuit 13. Further, the reproduced lowfrequency band carrier chrominance signal is supplied from the AFCcircuit to the frequency conversion circuit.

In case of this APC circuit, first, the ACC circuit 2 makes the signallevel of a low frequency band carrier chrominance signal constant andthen supplies the low frequency band carrier chrominance signal to thefrequency conversion circuit 3. Subsequently, a carrier chrominancesignal is obtained by effecting a frequency conversion operation in thefrequency conversion circuit 3. Further, a well-known automatic phasecontrol operation is performed on the thus obtained carrier chrominancesignal by a closed loop comprised of the frequency conversion circuit 3,the band-pass filter 4, the (1/2)-burst circuit 5, a comb type filter,which is composed of the 1-H delay line 6 and the adder 18, the burstgate circuit 14, the phase comparison circuit 13, the VCO 11, thefrequency conversion circuit 9 and the band-pass filter 10.

Furthermore, in this conventional APC circuit, the phase of a colorburst signal obtained by the burst gate circuit 14 and that of thereference chrominance subcarrier issued by the crystal oscillatingcircuit 12 are compared by the phase comparison circuit 13 which outputsa phase error signal to the VCO 11 to change the frequency of theoscillation thereof.

If the conventional APC circuit has infinite d.c. gain and does notinclude a delaying element such as a loop filter, a phase controloperation of controlling the change of the phase of the reproduced colorsignal (that is, the reproduced low frequency band carrier chrominancesignal) can be performed without delay time. The APC circuit, however,cannot have infinite d.c. gain. In other words, a practical APC circuithas inevitably a residual phase error. Further, in case where a phasedlock loop (PLL) type circuit is employed as the phase comparisoncircuit, a residual phase error is caused due to an operating principleof the PLL. Thus, the APC circuit effects an APC operation at a finitespeed of response.

Further, the reproduced color signal (that is, the reproduced lowfrequency band carrier chrominance signal) are usually mixed with noisesresulting from various origin, so that the signal-to-noise ratio (S/N)is deteriorated.

Furthermore, in case where the color burst signal obtained by the burstgate circuit 14 of the conventional APC circuit is mixed with noises,the phase comparison circuit 13 outputs a phase error signal caused dueto the presence of noises even when the phase of the color burst signalobtained by the burst gate circuit 14 is correct.

The APC circuit performs the APC operation in such a manner to cancelthe phase error signal having occurred in response to the noises whichare mixed with the color burst signal. Thus, in case where thereproduced color signal is mixed with noises, the phase of thereproduced color signal fluctuate as a result of the operation of theAPC circuit. Further, this results in the occurrence of color deviationin a reproduced image.

The color deviation thus generated in the reproduce image, however, canbe reduced to some extent by reducing the speed of response of the APCcircuit. Therefore, the APC operation has been performed by theconventional APC circuit under the conditions that an appropriate valueof the residual phase error is present.

However, in case of the APC circuit adapted to perform the APC operationin spite of the presence of the residual phase error, a stripe-shapedcolor deviating portion is generated at specific locations in an imagereproduced from the reproduced color signal sent from a color VTR inwhich, for example, what is called a head beat phenomenon may be caused.

As is well known in the art, in case where a head drum, which has twovideo heads at the positions of central symmetry on opposite sidesthereof, has an additional head at a specific location between the twovideo heads, this phenomenon may happen when the relative speed of amagnetic tape to the video heads is changed by vibration caused in thetape at the times of making the tape, which is in contact with the videoheads, touch the additional head and releasing the tape from theadditional head and further the APC circuit cannot respond to change infrequency of the reproduced color signal caused by the change of therelative speed of the tape.

Furthermore, the stripe-shaped color deviating portion generated due tosuch a phenomenon in the reproduced image is inconspicuous in case thatthe S/N is deteriorated. In contrast, in case that the S/N isameliorated by employing, for instance, a recursive type noise reducingcircuit including a frame memory or field memory, the color deviatingportion becomes clearly perceived.

In order to prevent the occurrence of the color deviation due to such aphenomenon, it is necessary to increase the speed of response of the APCcircuit as far as possible. However, as stated above, when the speed ofresponse of the APC circuit is increased, the problem of the colordeviation generated in the reproduced image due to the noises mixed upwith the color burst signal is brought up. Further, as above described,the conventional APC is adapted to perform the APC operation under theconditions that an appropriate value of the residual phase error ispresent. Therefore, the conventional APC circuit cannot eliminate orreduce the chance of the occurrence of the color deviation due to thehead beat phenomenon.

The present invention is accomplished to resolve the above describedproblem (hereunder sometimes referred to as a first problem) of theconventional color signal circuit.

It is accordingly an object (hereunder sometimes referred to as a firstobject) of the present invention to provide a color signal circuit whichcan easily obtain a color difference signal from which the residualphase error made by the APC operation of the APC circuit to be includedin a color signal.

Further, when the APC loop is unlocked due to some cause in the APCcircuit of which the response is delayed as described above, there iscaused the color deviation in the reproduced image until the APC circuitis restored to a normal APC operating condition.

The color deviation originated from the unlocking of the APC loop of theACC circuit is often caused due to, for example, the dropout of thereproduced color signal generated by repeating a duplicating operationin the VTR adapted to performing the processing of the low frequencyband carrier chrominance signal and the deterioration of the S/N.Especially, a color flicker can be easily caused in an upper portion ofthe reproduced image by the unlocking of the APC loop occuringimmediately posterior to the vertical synchronization signal due to thefact that a color burst signal is not present in a verticalsynchronization signal period.

By increasing the speed of response of the APC circuit as far aspossible, this problem can be resolved. However, as above described, theconventional APC is adapted to perform the APC operation under theconditions that an appropriate value of the residual phase error ispresent. Thus, the conventional APC circuit cannot eliminate or reducethe chance of the occurrence of the color flicker.

The present invention is accomplished to also resolve the abovedescribed problems of the conventional color signal circuit.

Further, in various equipment such as a color television receiver and acolor video tape recorder (VTR), has been used a conventional ACCcircuit, for example, as shown in FIG. 29.

In the conventional ACC circuit of FIG. 29, reference numeral 124denotes a video head; 125 a playback amplifier; 126 a variable gaincontrol circuit; 127 a frequency conversion circuit; 128 a comb typefilter; 129 a burst gate circuit; 130 an amplitude detection circuit;and 131 a mixer. Further, a signal reproduced by the video head 124 isamplified by the playback amplifier 125 and is thereafter supplied tothe variable gain control circuit 126.

Furthermore, this conventional ACC circuit, which includes a closed loopautomatic control system comprised of the variable gain control circuit126, the frequency conversion circuit 127, the comb type filter 128, theburst gate circuit 129 and the amplitude detection circuit 130, performsan automatic control operation in such a manner to make the amplitude ofthe color burst signal obtained by the burst gate circuit 129 constant.

This conventional ACC circuit, however, has drawbacks in that the range,in which the output signal level is constant, is narrow owing to thelimit to the operating range by the operating source voltage thereof andto the finiteness of the d.c. gain thereof and that the signal level ofthe output signal is fluctuated when the color burst signal inputthereto is mixed with a noise.

Thus, the conventional ACC circuit is made to have a relatively largetime constant of the loop filter in order to reduce the fluctuation ofthe signal level of the output signal caused due to the noise.

Further, in case of the VTR of which a plurality of video heads aresequentially switched from each other with a lapse of time, the colorflicker is generated in the reproduced image and thus the picturequality of the reproduced image is deteriorated if there is anydifference among the signal levels of the signals reproduced by theplurality of the video heads.

Even in case where there is any difference among the signal levels, ifthe difference can be compensated by the operation of the ACC circuit,such difference is no consideration. However, as illustrated in FIG. 30,the input/output characteristic of the conventional ACC circuit is notsufficient to compensate the difference among the signal levels of thereproduced color signals. Thus, in case of employing the conventionalACC circuit, the color flicker often occurs.

Further, even in case where the color flicker is generated in thereproduced image due to the above described cause, if the S/N of thecolor signal is deteriorated, the color flicker may be masked by thenoise, so that viewers may not mind the color flicker. In contrast, ifthe S/N of the reproduced color signal is ameliorated by using, forinstance, the recursive type noise reducing circuit which includes theframe memory or the field memory, the color flicker becomes clearlyperceived in the reproduced image by the viewers.

The present invention is accomplished to also resolve this problem ofthe conventional color signal circuit having the ACC circuit.

It is accordingly another object (hereunder sometimes referred to as asecond object) of the present invention to provide a color signalcircuit which can eliminate or reduce the chance of the occurrence ofthe color flicker.

Further, in various equipment such as a color television receiver and acolor VTR, the conventional process of controlling hue is performed bychanging the phase of the carrier used for obtaining the carrierchrominance signal or changing the phase of the color burst signal.

The conventional phase shifter for shifting the phase of the color burstsignal and that of the carrier used for obtaining the carrierchrominance signal is usually comprised of an analog circuit. Thus, thecharacteristics of the conventional phase shifter are liable to largelyvary in response to change in ambient temperature. In the prior art, itis therefore very difficult to obtain a hue control device which canstably control the hue.

Furthermore, in the prior art, there is no means for easily controllingthe hue of the color indicated by the color signal which is in the formof the color difference signal. Thus, in the conventional equipmentwhich processes the color difference signal, the hue cannot be easilycontrolled.

The present invention is accomplished to also eliminate this drawback ofthe prior art.

It is therefore still another object (hereunder sometimes referred to asa third object) of the present invention to provide a color signalcircuit which can easily control the hue.

SUMMARY OF THE INVENTION

To achieve the foregoing first object and in accordance with a firstaspect of the present invention, there is provided a color signalcircuit which comprises a conversion means for converting two colordifference signals, which are equivalent to two color difference signalsto be obtained by performing the color demodulation of a color signal byusing two color difference axes intersecting perpendicularly to eachother, into a color amplitude signal corresponding to the amplitude ofthe color signal and a color phase signal corresponding to the phase ofthe color signal and a signal processing means for processing at leasteither of the color amplitude signal and the color phase signal.

In accordance with a second aspect of the present invention, there isprovided a color signal circuit which comprises a conversion means forconverting two color difference signals, which are equivalent to twocolor difference signals to be obtained by performing the colordemodulation of a color signal by using two color difference axesintersecting perpendicularly to each other, into a color amplitudesignal corresponding to the amplitude of the color signal and a colorphase signal corresponding to the phase of the color signal, aphase-deviation-quantity signal generating means for generating a phasedeviation quantity signal corresponding to the quantity of the phasedeviation of the color phase signal outputted from the conversion meansin response to a color synchronizing signal, a substration means forperforming a subtration operation by letting a value indicated by thecolor phase signal outputted from the conversion means be a minuend andalso letting a value indicated by the phase deviation quantity signaloutputted from the phase-deviation-quantity signal be a subtrahend and acolor difference signal generating means for generating two colordifference signals on the basis of the color amplitude signal and thecolor phase signal outputted from the subtraction means.

In accordance with a third aspect of the present invention, there isprovided a color signal circuit which comprises a data conversion meansfor converting digital data indicated by two color difference signals,which are equivalent to two color difference signals to be obtained byperforming the color demodulation of a carrier chrominance signalincluding a color burst signal by using two color difference axesintersecting perpendicularly to each other, into digital data indicatedby a color amplitude signal corresponding to the amplitude of the colorsignal and digital data indicated by a color phase signal correspondingto the phase of the color signal, a phase-deviation-quantity datagenerating means for generating digital data representing the quantityof the phase deviation of the color burst signal outputted from the dataconversion means correspondingly to digital data indicated by the colorburst signal, a substraction means for performing a substractionoperation by letting digital color phase data indicated by the colorphase signal outputted from the data conversion means be a minuend andalso letting phase deviation quantity data indicated by the phasedeviation quantity signal outputted from the phase-deviation-quantitysignal be a subtrahend and a color difference signal generating meansfor generating two color difference signals on the basis of the colordigital amplitude data and the color phase data outputted from thesubtraction means.

Thus, an operation (Asin θ/Acos θ) is first performed on data equivalentto the data indicated by two input color difference signals Asin θ andAcos θ to be obtained when the color demodulation of the carrierchrominance signal having an amplitude A and a phase θ is effected byusing the two color difference axes. Then, the color phase signalcorresponding to the phase θ is obtained from the result of theoperation tan θ.

Further, a signal corresponding to sin θ (or cos θ) is obtained from thecolor phase signal. Then, an operation [Asin θ/sin θ (or Acos θ/cos θ)]is performed on the thus obtained signal and the input color differencesignal Asin θ (or Acosθ). Thus, the color amplitude signal correspondingto the amplitude A is obtained from the result of this operation.

Furthermore, the phase θ of the color burst signal included in the inputcolor difference signal is evaluated and is then supplied to thewell-known recursive noise reducer type digital filter which includesthe frame memory (or the field memory) and a feedback ratio circuit.Thus, the phase deviation quantity signal corresponding to the quantityof the phase deviation of the color burst signal is generated.

Subsequently, the subtraction is effected by letting a value indicatedby the color phase signal be a minuend and also letting a valueindicated by the phase deviation quantity signal be a subtrahend. Thus,the color phase signal obtained by compensating the phase deviation isgenerated.

Thereby, can be easily obtained the color difference signal in which theresidual phase error included in the color signal is eliminated byperforming the APC operation of the APC circuit. Thus, the first problemof the conventional color signal circuit can be preferably resolved.

To achieve the foregoing second object and in accordance with a fourthaspect of the present invention, there is provided a color signalcircuit which comprises a conversion means for converting two colordifference signals, which are equivalent to two color difference signalsto be obtained by performing the color demodulation of a color signal byusing two color difference axes intersecting perpendicularly to eachother, into a color amplitude signal corresponding to the amplitude ofthe color signal and a color phase signal corresponding to the phase ofthe color signal, a difference signal generating means for generating inresponse to a color synchronizing signal a difference signalrepresenting the difference of a current color signal outputted by theconversion means from the average or mean of the past color phasesignals, a nonlinear signal processing means for nonlinearly changing anoutput thereof depending on the magnitude of the difference signalgenerated by the difference signal generating means and the currentcolor phase signal, a subtraction means for performing a subtractionoperation by letting a value indicated by the current color phase signaloutputted from the conversion means be a minuend and also letting avalue indicated by the output signal of the nonlinear processing meansbe a subtrahend and a color difference signal generating means forgenerating two color difference signals on the basis of the coloramplitude signal and the color phase signal outputted from thesubtracting means.

Further, in accordance with a fifth aspect of the present invention,there is provided a color signal processing circuit, comprising a signalconversion means for converting two color difference signals, which areequivalent to two color difference signals to be obtained by performingcolor demodulation of a color signal by using two color difference axesintersecting perpendicularly to each other, into a color amplitudesignal corresponding to the amplitude of the color signal and a colorphase signal corresponding to a phase of the color signal; a differencesignal generating means for generating, in response to a colorsynchronizing signal, a difference signal representing the differencebetween a current color signal outputted by said signal conversion meansand the average of past color phase signals; a nonlinear signalprocessing means for nonlinearly changing an output thereof depending onthe magnitude of the difference signal generated by said differencesignal generating means and the current color phase signal; a signalmodification means for generating and outputting a modified color phasesignal which represents data to be obtained by subtracting a valueindicated by the output signal of said nonlinear processing means from avalue indicated by the current color phase signal outputted from saidsignal conversion means; and a color difference signal generating meansfor generating two color difference signals on the basis of the coloramplitude signal and the modified color phase signal outputted from saidsignal modification means.

Furthermore, in accordance with a sixth aspect of the present invention,there is provided a color signal processing circuit comprising a signalconversion means for converting two color difference signals, which areequivalent to two color difference signals to be obtained by performingcolor demodulation of a color signal by using two color difference axesintersecting perpendicularly to each other, into a color amplitudesignal corresponding to the amplitude of the color signal and a colorphase signal corresponding to the phase of the color signal; adifference signal generating means for generating in response to a colorsynchronizing signal a difference signal representing the differencebetween a current color signal outputted by said signal conversion meansand the average of the past color phase signals; a nonlinear signalprocessing means for nonlinearly changing an output thereof depending onthe magnitude of the difference signal generated by the differencesignal generating means and the current color phase signal; a firstsignal modification means for generating and outputting a first modifiedcolor phase signal which represent data obtained by subtracting a valueindicated by the output signal of said nonlinear processing means from avalue indicated by a current color phase signal outputted from saidsignal conversion means; a phase-deviation-quantity signal generatingmeans for generating a phase deviation signal corresponding to a phasedeviation quantity of the color phase signal outputted from saidconversion means; a second signal modification means for generating andoutputting a second modified color phase signal which represents data tobe obtained by subtracting data indicated by the phase deviationquantity signal, which is outputted from said phase-deviation-quantitysignal generating means, from data indicated by the first modified colorphase signal outputted from said first modified signal modificationmeans; and a color difference signal generating means for generating twocolor difference signals on the basis of the color amplitude signal andthe second modified color phase signal outputted from said second signalmodification means.

Thus, similarly as in cases of the color signal circuits in accordancewith the first, second and third aspects of the present invention, anoperation (Asin θ/Acos θ) is first performed on data equivalent to thedata indicated by two input color difference signals Asin θ and Acos θto be obtained when the color demodulation of the carrier chrominancesignal having an amplitude A and a phase θ is effected by using the twocolor difference axes. Then, the color phase signal corresponding to thephase θ is obtained from the result of the operation tan θ.

Further, a signal corresponding to sin θ (or cos θ) is obtained from thecolor phase signal. Then, an operation [Asin θ/sin θ (or Acos θ/cos θ)]is performed on the thus obtained signal and the input color differencesignal Asin θ (or Acos θ). Thus, the color amplitude signalcorresponding to the amplitude A is obtained from the result of thisoperation.

Furthermore, the phase θ of the color burst signal included in the inputcolor difference signal is evaluated and is then supplied to thewell-known recursive noise reducer type digital filter which includesthe frame memory (or the field memory) and a feedback ratio circuit.Thus, the difference signal corresponding to the difference of thecurrent phase of the color burst signal from the average of the phase ofthe past color burst signal is generated.

Then, the difference signal is supplied to the nonlinear signalprocessing means of which the output changes depending on the magnitudeof the difference signal.

Subsequently, the subtraction is effected by letting data indicated bythe color phase signal be a minuend and also letting data indicated bythe output of the nonlinear signal processing means be a subtrahend.Thus, the color phase signal obtained by compensating the phasedeviation is generated.

Further, as a result of supplying the phase θ of the color burst signalincluded in the input color difference signal and evaluated as abovedescribed to the well-known recursive noise reducer type digital filterwhich includes the frame memory (or the field memory) and a feedbackratio circuit, the phase deviation quantity signal corresponding to thephase deviation quantity of the color burst signal is generated.

Subsequently, the subtraction is effected by letting data indicated bythe compensated color phase signal obtained by subtracting the dataindicated by the output signal of the nonlinear signal processing meansfrom that indicated by the color phase signal as above described be aminuend and also letting data indicated by the phase deviation quantitysignal be a subtrahend. Then, the color signal having predetermined formis generated by using the color phase signal obtained by compensatingthe phase deviation and the color amplitude signal.

Thereby, the change in phase of the color phase signal, which is largeenough to cause the color flicker in the reproduced image, can be easilyreduced. Further, can be easily obtained the color difference signal inwhich the residual phase error included in the color signal iseliminated by performing the APC operation of the APC circuit. Thus, thesecond problem of the conventional color signal circuit can bepreferably resolved.

However, the color signal circuits according to the first to sixthaspects of the present invention have the drawback, which will beexplained later in detail, that in case where an object to be processedis switched to another color signal from a different or new signalsource, when the phase of the color burst signal corresponding to thecolor signal from the new signal source is largely changed from that ofthe color burst signal corresponding to the color signal from the formersignal source, it takes relatively long time till the color signalcircuit returns to normal conditions. The present invention isaccomplished to further eliminate this drawback.

Therefore, it is further object (hereunder sometimes referred to as afourth object) of the present invention is to provide a color signalcircuit which can quickly return to the normal conditions even in casewhere an object to be processed is switched to another color signal froma new signal source and further the phase of the color burst signalcorresponding to the color signal from the new signal source is largelychanged from that of the color burst signal corresponding to the colorsignal from the former signal source.

To achieve the foregoing fourth object and in accordance with a seventhaspect of the present invention, there is provided a color signalprocessing circuit comprising an average-value-signal generating meansfor generating and outputting an average-value-signal which representsan average or mean of values indicated by past color phase signals, theaverage being obtained by supplying data indicated by the color phasesignal, which corresponds to a phase of a color signal obtained on thebasis of two color difference signals having a signal form similar totwo color difference signals to be obtained by effecting colordemodulation of a color signal by using two color difference axesintersecting perpendicularly to each other, during a period of a colorsynchronizing signal sent a recursive type digital filter which includesa memory capable of storing a signal having a period obtained bymultiplying a vertical scanning period by an integer, said digitalfilter further including an arithmetic circuit and a feedback ratiocircuit having a high feedback ratio; a count-signal generating meansfor generating and outputting, during every vertical scanning period, acount signal representing a number of data indicated by the color phasesignal on the basis of a current color synchronizing signal, from whichthe average value indicated by the average-value-signal is subtracted toobtain a difference equal to or larger than a predetermined value; and afeedback-ratio-control-signal generating means for generating a controlsignal to reduce the feedback ratio of the feedback ratio circuit when anumber of vertical scanning periods, in which the number of dataindicated by the count signal is in excess of a predetermined value,exceeds a predetermined value.

Further, in accordance with an eight aspect of the present invention,there is provided a color signal processing circuit comprising: anaverage-value-signal generating means for generating and outputting anaverage-value-signal which represents an average or mean of valuesindicated by past color phase signals, the average being obtained bysupplying data indicated by the color phase signal, which corresponds toa phase of the color signal obtained on the basis of two colordifference signals having a signal form similar to two color differencesignals to be obtained by effecting the color demodulation of a colorsignal by using two color differences axes intersecting perpendicularlyto each other, during a period of a color synchronizing signal sent to arecursive type digital filter which includes a memory capable of storinga signal having a period obtained by multiplying a vertical scanningperiod by an integer, said digital filters further including anarithmetic circuit and a feedback ratio circuit having a high feedbackratio; a count-signal generating means for generating and outputting,during every vertical scanning period, a count signal representing anumber of data indicated by the dolor phase signal on the basis of acurrent color synchronizing signal, from which the average valueindicated by the average-value-signal is subtracted to obtain adifference equal to or larger than a predetermined value; afeedback-ratio-control-signal generating means for generating a controlsignal to reduce the feedback ratio of the feed back ratio circuit whena number of vertical scanning periods, in which the number of dataindicated by the count signal is in excess of a predetermined value,exceeds a predetermined value; and a phase-deviation-quantity signalgenerating means for generating a phase deviation quantity signalcorresponding to a quantity of a phase deviation of a color phase signaloutputted from the digital filter.

Namely, in the color signal circuit, the data on the average of thevalues indicated by the past color phase signals is first obtained bysupplying data indicated by the color phase signal, which corresponds tothe phase of the color signal obtained on the basis of two colordifference signals having the signal form similar to the two colordifference signals to be obtained by effecting the color demodulation ofa color signal by using two color difference axes intersectingperpendicularly to each other, of the period of the color synchronizingsignal to the recursive type digital filter which includes a memorycapable of storing a signal having a period obtained by multiplying avertical scanning period by an integer, an arithmetic circuit and afeedback ratio circuit having a high feedback ratio.

Then, the data indicated by the color phase signal based on the currentcolor synchronizing signal is compared with the data generated by theaverage value data generating means indicating the average of the valuesindicated by the past color phase signal. Further, the number of thedata indicated by the color phase signal, of which the difference fromthe average value of the past color phase signal is equal to or largerthan a predetermined value, is counted every vertical scanning period.

Subsequently, the feedback ratio of the feed back ratio circuit isreduced when the number of the vertical scanning periods, in which thecount obtained by the first counting means is in excess of apredetermined value, exceeds a predetermined value. Thus, theresponsiveness is improved.

Thereby, the foregoing drawback of the color signal circuits accordingto the first to sixth aspects of the present invention can be favorablyeliminated.

To achieve the foregoing second object and in accordance with a ninthaspect of the present invention, there is further provided a colorsignal processing circuit comprising: a signal conversion means forconverting two color difference signals, which are equivalent to twocolor difference signals to be obtained by performing color demodulationof a color signal by using two color difference axes intersectingperpendicularly to each other, into a color amplitude signalcorresponding to an amplitude of the color signal and a color phasesignal corresponding to a phase of the color signal; a noise reducingmeans for reducing noises in the color amplitude signal obtainedcorrespondingly to a color synchronizing signal and for outputting thecolor amplitude signal, the noise in which is reduced; acoefficient-signal generating means for generating a signal representinga coefficient such that when the amplitude of the color amplitude signaloutputted from the noise reducing means is multiplied by thecoefficient, a predetermined constant value of the amplitude isobtained; a product-signal generating means for generating a signalrepresenting a product obtained by multiplying the color amplitudesignal fed from said noise reducing means by the coefficient fed fromsaid coefficient-signal generating means; a color amplitude signalsupplying means for supplying the color amplitude signal outputted fromsaid signal conversion means to said product-signal generating means;and a color difference signal generating means for generating apredetermined color difference signal on the basis of the coloramplitude signal outputted from said product-signal generating means andthe color phase signal outputted from said signal.

Thus, similarly as in cases of the color signal circuits in accordancewith the first to sixth aspects of the present invention, an operation(A sin θ/A cos θ) is first performed on data equivalent to the dataindicated by two input color difference signals A sin θ and A cos θ tobe obtained when the color demodulation of the carrier chrominancesignal having an amplitude A and a phase θ is effected by using the twocolor difference axes. Then, the color phase signal corresponding to thephase θ is obtained from the result of the operation tan θ.

Further, a signal corresponding to sin θ (or cos θ) is obtained from thecolor phase signal. Then, an operation [A sin θ/ sin θ (or A cos θ/ cosθ)] is performed on the thus obtained signal and the input colordifference signal A sin θ (or A cos θ). Thus, the color amplitude signalcorresponding to the amplitude A is obtained from the result of thisoperation.

Then, the value of the amplitude of the color burst signal included inan input color difference signal is evaluated and a signal representingthe evaluated value of the amplitude of the color burst signal isfurther supplied to the well-known recursive noise reducer type digitalfilter which includes a frame memory (or a field memory), a feedbackratio circuit and a subtracter, and thus generates the amplitude signalcorresponding to the color burst signal from which the noise iseliminated.

Subsequently, the amplitude signal corresponding to the color burstsignal, from which the noise is eliminated, is supplied to thecoefficient generating means capable of generating a coefficient in sucha manner that a predetermined amplitude value is obtained when the valueof the amplitude of the color burst signal, from which the noise iseliminated, outputted from the noise reducing means is multiplied by thecoefficient. Thus, the coefficient is generated.

Further, a signal indicating the coefficient generated by thecoefficient generating means and the color amplitude signal outputted bythe conversion means are supplied to the multiplication means, whereupona color amplitude signal, of which the amplitude is modified orcompensated, is generated.

Then, a color signal having the predetermined signal form is generatedby using the color amplitude signal, of which the amplitude is thusmodified, and the color phase signal.

Thereby, can be eliminated the color flicker and the color unevennessoccurring in the reproduced image in case of the color signal circuitusing the conventional ACC circuit. Further, the integration of thecolor signal circuit can be easily realized because an object to beprocessed is a digital signal. Thus, the unevenness in characteristicsof the color signal circuits can be easily eliminated. Furthermore, themanufacturing cost of the color signal circuit can be considerably savedbecause a storage, of which the storage capacity is 500 words or so, canbe used as the frame memory.

To achieve the foregoing third object and in accordance with a tenthaspect of the present invention, there is provided a color signalprocessing circuit comprising:

signal conversion means for converting two color difference signals,which are equivalent to two color difference signals to be obtained byperforming color demodulation of a color signal by using two colordifference axes intersecting perpendicularly to each other, into a coloramplitude signal corresponding to an amplitude of the color signal and acolor phase signal corresponding to a phase of the color signal; asignal modification means for generating and outputting a modified colorphase signal which represents data to be obtained by adding phaseshifting data to or subtracting the phase shifting data from dataindicated by the color phase signal outputted from said signalconversion means; and a color signal generating means for generating apredetermined color signal on the basis of the color amplitude signaland the color phase signal outputted from said signal modificationmeans.

Thus, similarly as in cases of the color signal circuits in accordancewith the first to sixth and ninth aspects of the present invention, anoperation (A sin θ/A cos θ) is first performed on data equivalent to thedata indicated by two input color difference signals A sin θ and A cos θto be obtained when the color demodulation of the carrier chrominancesignal having an amplitude A and a phase θ is effected by using the twocolor difference axes. Then, the color phase signal corresponding to thephase θ is obtained from the result of the operation tan θ.

Further, a signal corresponding to sin θ (or cos θ) is obtained from thecolor phase signal. Then, an operation [A sin θ/ sin θ (or A cos θ/ cosθ)] is performed on the thus obtained signal and the input colordifference signal A sin θ (or A cos θ). Thus, the color amplitude signalcorresponding to the amplitude A is obtained from the result of thisoperation.

Then, the phase shifting data is added to or subtracted from the dataindicated by the color phase signal generated from an input colordifference signal. Thus, the phase-shifted color phase signal isgenerated.

Thereafter, a color signal having a predetermined form is generated byusing the phase-shifted color phase signal and the color amplitudesignal.

Thereby, the hue can be easily controlled with respect to the colordifference signal of which the hue control cannot be easily performed bythe conventional color signal circuit. Further, the hue can beaccurately controlled because the hue control is effected by the digitalsignal processing. Moreover, the variation in phase shifting angle dueto the change in ambient temperature can be prevented. Furthermore, thehue control circuit can be easily constructed by using integratedcircuits. Incidentally, a phase shifting circuit provided in an encoderportion of the conventional color signal circuit can be omitted. Thus,can be easily provided a color signal circuit which can favorablyresolve the drawback of the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, objects and advantages of the present invention willbecome apparent from the following description of preferred embodimentswith reference to the drawings in which like reference charactersdesignate like or corresponding parts throughout several views, and inwhich:

FIGS. 1, 2 and 3 are schematic block diagrams each showing theconstruction of a different color signal processing circuit embodyingthe present invention;

FIGS. 4(a)-4(c) and 5(a)-5(c) are diagrams for illustrating an operationof the circuits of FIGS. 1-3;

FIG. 6 is a graph for showing the characteristic of a feedback ratiocircuit;

FIG. 7 is a schematic block diagram for showing the construction of agenerating circuit for generating data representing color amplitude Aand data representing color phase θ according to the present inventionother than the circuits of FIGS. 1-3;

FIGS. 8 and 9 are diagrams for illustrating an operation of the circuitof FIG. 7;

FIG. 10 is a schematic block diagram for showing the construction of theconventional APC circuit;

FIGS. 11-15 are schematic block diagrams for showing the construction ofother color signal circuits embodying the present invention;

FIG. 16 is a graph for showing the characteristic of a feedback ratiocircuit of the embodiments of FIGS. 11-15 and 31;

FIGS. 17-20 are graphs for showing the input/put characteristics ofnonlinear signal processing circuits of FIGS. 12-15;

FIGS. 21(a)-21(e) is a diagram for illustrating an operation of theembodiment of FIG. 11;

FIGS. 22(a)-22(e) is a diagram for illustrating an operation of theembodiment of FIG. 13;

FIGS. 23(a)-23(d) and 24(a)-24(c) are diagrams for illustrating anoperation of the embodiment of FIG. 15;

FIGS. 25 and 28 are schematic block diagrams for showing other colorsignal circuits embodying the present invention;

FIGS. 26 and 27 are schematic block diagrams for showing controlcircuits having different construction;

FIG. 29 is a schematic block diagram for showing the construction of theconventional ACC circuit;

FIG. 30 is a graph for showing the input/output characteristic of theconventional ACC circuit of FIG. 29;

FIG. 31 is a schematic block diagram for showing the construction offurther another color signal circuit embodying the present invention;

FIGS. 32(a)-32(h) is a diagram for illustrating an operation of theembodiment of FIG. 31; and

FIGS. 33-35 are schematic block diagrams for showing the construction ofother color signal circuits embodying the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the preferred embodiments of the present invention will bedescribed in detail by referring to the accompanying drawings.

In FIGS. 1-3 and 7, reference numeral 19 designates an input terminalfor receiving digital data indicated by one (hereunder described as acolor difference signal of red R-Y) of two color difference signalshaving signal forms similar to the forms of two color difference signalsto be obtained by effecting the color demodulation of a carrierchrominance signal by using two color difference axes intersectingperpendicularly to each other; and 20 another input terminal forreceiving digital data indicated by the other (hereunder described as acolor difference signal of blue B-Y) of the two color differencesignals.

Further, in FIGS. 1-3 for respectively showing different color signalcircuits embodying the present invention, reference numerals 21, 25 and26 denote dividers; 27 an adder; 29 a burst gate circuit; 30, 31, 33 and35 subtracters; 32 a feedback ratio circuit; 38 and 39 multipliers; 34 aframe memory; 22-24, 28, 36 and 37 arithmetic operation circuits; and 40and 41 output terminals. Incidentally, the composing element 34 may be afield memory.

Referring to FIGS. 1-3, the digital data indicated by the colordifference signal R-Y, which is one of the two color difference signalsR-Y and B-Y having the signal forms similar to those of the two colordifference signals Asin θ and Acos θ to be obtained by performing thecolor demodulation of a carrier chrominance signal having an amplitude Aand a phase θ by using two color difference axes intersectingperpendicularly to each other, is supplied to the input terminal 19. Onthe other hand, the digital data indicated by the other color differencesignal B-Y is supplied to the input terminal 20.

In the circuits of FIGS. 1-3, the digital data indicated by the signalR-Y is supplied to the divider 21 as a dividend and on the other hand,the digital data indicated by the signal B-Y is supplied to the divider21 as a divisor. Then, the divider 21 performs an operation representedby the expression Asin θ/Acos θ (=tan θ) and outputs data correspondingto the results of the operation, namely, tan θ to the arithmeticoperation circuit 22.

Further, the circuit 22 generates data representing the color phase θbased on the data tan θ supplied thereto and supplies the datarepresenting the color phase θ to the burst gate circuit 29 and thedivider 35. Moreover, in case of the embodiment of FIG. 1, the datarepresenting the color phase θ is also supplied to the circuits 23 and24. Furthermore, in case of the embodiment of FIG. 2, the data θ is alsosupplied to the circuit 24. Further, in case of the embodiment of FIG.3, the data θ is also supplied to the circuit 23.

In the embodiments of FIGS. 1 and 2, the digital data represented by theexpression (B-Y=Acos θ) and inputted to the terminal 20 is supplied tothe divider 26 as a dividend. Further, the divider 26 effects anoperation represented by the expression (Acos θ/cos θ) and outputs thedata indicating the color amplitude A.

In case of the embodiment of FIG. 1, the data representing the coloramplitude A outputted from the divider 26 is supplied to the adder 27.Further, in case of the embodiment of FIG. 2, the data representing thecolor amplitude A outputted from the divider 26 is supplied to themultipliers 38 and 39.

Further, in the embodiments of FIGS. 1 and 3, the digital datarepresented by the expression (R-Y=A sin θ) supplied to the inputterminal 19 is applied to the divider 25 as a dividend. Then, thedivider 25 effects the operation represented by the expression (Asinθ/sin θ) and further outputs the data representing the color amplitudeA.

Moreover, in the embodiment of FIG. 1, data indicating 2A is outputtedfrom the adder 27 and is further divided by 2 in the circuit 28. Thedata indicating the color amplitude A is thus obtained and is then fedto the multipliers 38 and 39.

If data on the color burst signal is made to be included in a specificportion of each of the color difference signals supplied to the inputterminals 19 and 20 in each horizontal blanking interval, phase data ofthe color burst signal can be outputted from the circuit 22correspondingly to the specific portion of the color difference signalin each horizontal blanking interval.

Next, in FIG. 7, reference numeral 19 designates an input terminal forreceiving digital data indicated by one (hereunder described as a colordifference signal of red R-Y (=Asin θ)) of two color difference signalshaving signal forms similar to the forms of two color difference signalsto be obtained by effecting the color demodulation of a carrierchrominance signal having an amplitude A and a phase θ by using twocolor difference axes intersecting perpendicularly to each other; and 20another input terminal for receiving digital data indicated by the other(hereunder described as a color difference signal of blue B-Y (=Acos θ))of the two color difference signals. Incidentally, the digital datasupplied to the input terminals 19 and 20 are data represented by two'scomplement.

Further, it is supposed that digital data indicated by the color burstsignal is present at a specific position in at least one of the colordifference signals supplied to the input terminals 19 and 20 in thehorizontal blanking interval.

In this figure, reference numerals 21, 22, 25, 26 and 55 denotesarithmetic operation circuits; 27 and 46 adders; 42 and 43 absolutevalues circuits; 44 an inverter; 45, 51-53 and 56 switches; 47 and 48logic circuits; 49 and 50 a logical zero detection circuit for detectinga logical value 0; and 54 an OR circuit.

Referring to FIG. 7, a signal indicating a sign bit of digital dataindicated by the R-Y signal supplied to the terminal 19 is supplied tothe absolute value circuit 42 and the logic circuits 47 and 48. Further,a signal indicating a sign bit of digital data indicated by the B-Ysignal supplied to the terminal 20 is supplied to the absolute valuecircuit 43 and the logic circuits 47 and 48.

In the circuit 21 to which the output data Asin θ is supplied from theabsolute value circuit 42 as a dividend, a division operation isperformed by using the data Acos θ outputted from the absolute valuecircuit 43 as a divisor. Further, the result tan θ of the division isfed to the arithmetic operation circuit 22.

Then, the circuit 22 produces data corresponding to the phase θ from thedata indicating tan θ supplied thereto and then outputs the thusproduced data to a fixed contact L of the switch 45 and the inverter 44which inverts the sign of the data indicating the color phase θ andfurther supplies the data indicating the inverted phase (-θ) to a fixedcontact H of the switch 45.

A movable contact V of the switch 45 is switched to either of the fixedcontacts L and H in accordance with a switch control signal outputtedfrom the circuit 47. In FIG. 8, when a control signal output to theswitch 45 has a low level L, the movable contact V of the switch 45 isswitched to the fixed contact L. In contrast, when the control signaloutput to the switch 45 has a high level H, the contact V of the switch45 is switched to the contact H.

The logic circuit 47 is adapted to supply a switch control signal havinga level as listed in FIG. 8 to the switch 45 in accordance with thecombination of the level H or L of the sign bit of the digital data(hereunder sometimes referred to simply as R-Y data) indicated by theR-Y signal supplied from the terminal 19 and that H or L of the sign bitof the digital data (hereunder sometimes referred to simply as B-Y data)indicated by the B-Y signal supplied from the terminal 20.

Further, the phase angles 0 and 180 degrees as indicated in FIG. 8 arethose of a signal to be supplied to the adder 46, which will bedescribed later, in accordance with the combination of the level H or Lof the sign bit of the R-Y data and that H or L of the sign bit of theB-Y data.

Incidentally, as is seen from FIGS. 1-3 and 7, the data representing thecolor phase θ outputted from the operation circuit 22 is furtherprocessed by a signal processing portion composed of the inverter 44,the switch 45, the adder 46, the logical circuits 47 and 48, the logicalzero detection circuits 49 and 50 and the switch 51 and is thenoutputted to an external circuit. This is because the circuit 22 canperform the operation with respect to the phase angle θ of the data tanθ inputted thereto only ranging from 0 to 90 degrees in spite of thefact that the phase θ" of the data tan θ" inputted thereto ranges from 0to 360 degrees.

Thus, the signal processing portion comprised of the inverter 44, theswitch 45, the adder 46, the logical circuits 47 and 48, the logicalzero detection circuits 49 and 50 and the switch 51 is adapted to outputthe data indicating the phase angle θ (hereunder sometimes referred toas the color phase data θ) according to the range of the phase angle θ"of the data tan θ" inputted to the circuit 22 as follows. Namely, whenthe angle θ" of the data tan θ" inputted to the circuit 22 is within therange between 0 and 90 degrees, the data θ" outputted from the circuit22 is further outputted from the signal processing portion without beingchanged as the color phase data θ. Further, when the angle θ" of thedata tan θ" inputted to the circuit 22 is within the range between 90degrees and 180 degrees, data indicating the value obtained bysubtracting the data θ' outputted from the circuit 22 from 180 degreesis outputted from the signal processing portion as the color phase dataθ. Moreover, when the angle θ" of the data tan θ" inputted to thecircuit 22 is within the range between 180 degrees and 270 degrees, dataindicating the value obtained by adding the data θ" outputted from thecircuit 22 to 180 degrees is outputted from the signal processingportion as the color phase data θ. Furthermore, when the angle θ" of thedata tan θ" inputted to the circuit 22 is within the range between 270degrees and 360 degrees, data indicating the value obtained by invertingthe sign of the data θ" outputted from the circuit 22 is outputted fromthe signal processing portion as the color phase data θ.

On the other hand, the data θ" outputted from the circuit 22 is suppliedto the adder 46 as the color phase data θ or (-θ) through the switch 45,of which the movable contact V is switched in accordance with the switchcontrol signal above described by referring to FIG. 8.

Further, the data indicating the phase angle 0 or 180 degrees asindicated in the rightmost column of FIG. 8 is fed to the adder 46 whichoutputs a signal representing the sum of the two kinds of data inputtedthereto to a fixed contact 1 of the switch 51.

Incidentally, data indicating the phase angle 0, data indicating thephase angle 90 degrees, data indicating the phase angle 180 degrees anddata indicating the phase angle 270 degrees are respectively supplied tofixed contacts 2, 3, 4 and 5 of the switch 51.

Each of the logical zero detection circuit 49, to which the output dataof the absolute value circuit 42 is fed, and the logical zero detectioncircuit 50, to which the output data of the absolute value circuit 43 isfed, supplies output signals having a high level to the logic circuit 48when digital data inputted thereto has a logical value 0.

Further, the signal indicating the sign bit of the R-Y data and thatindicating the sign bit of the B-Y data are also supplied to the logiccircuit 48 which generates a switch control signal such that outputsignals 1, 2, 3, 4 and 5 are selectively outputted from the switch 51according to the combination of the sign bits of the R-Y data and theB-Y data and the outputs of the circuits 49 and 50. Incidentally, inFIG. 9, characters H and L denotes a signal having a high level and asignal having a low level, respectively.

Further, the data outputted from the movable contact of the switch 51 isoutputted as the data representing the color phase θ.

Further, the data representing the color phase data θ is outputted fromthe switch 51 is also supplied to the circuits 23 and 24. Thus, the datahaving an absolute value of sin θ is fed from the circuit 23 to thecircuit 25 as a divisor and on the other hand the data having anabsolute value of cos θ is fed from the circuit 24 to the circuit 26 asa divisor.

To the circuit 25, the digital data indicated by the R-Y signal issupplied from the absolute value circuit 42 as a dividend. The operationcircuit 25 effects an operation expressed by the equation Asin θ/sin θand thereafter outputs the data representing the color amplitude A to afixed contact L of the circuit 52.

Similarly, To the circuit 26, the digital data indicated by the B-Ysignal is supplied from the absolute value circuit 43 as a dividend. Theoperation circuit 26 effects an operation expressed by the equation Acosθ/cos θ and thereafter outputs the data representing the color amplitudeA to a fixed contact L of the circuit 53.

Further, data corresponding to 0 is supplied to fixed contacts H of theswitches 52 and 53. Moreover, the control operation of a movable contactV of the switch 52 is performed in accordance with the output data ofthe circuit 49. Furthermore, the control operation of a movable contactV of the switch 53 is performed in accordance with the output data ofthe circuit 50.

Incidentally, the output data of the circuits 49 and 50 are used tocontrol the switching operation of a movable contact V of the switch 56,which will be described later, through the OR circuit 54.

After the data representing the color amplitude A outputted from themovable contact of the switch 52 is added to the data sent from themovable contact V of the switch 53 by the adder 27, the resultant datais supplied to a fixed contact L of the switch 56 and to the circuit 55.Further, data representing a color amplitude 2A obtained by doubling thedata from the adder 27 in the circuit 55 is fed to a fixed contact ofthe switch 56.

Then, the data representing the color amplitude 2A is outputted from amovable contact V of the switch 56.

In the embodiments of FIGS. 1-3 and 7, the data representing the colorphase θ outputted from the circuit 22 in a specific portion of thehorizontal blanking interval of the color difference signal is datarepresenting the phase θ' of the color burst signal which is present inthe horizontal blanking interval of the color difference signal.

Further, for instance, a latch circuit may be used as the burst gatecircuit 29, to which is the color phase data is supplied, in theembodiments of FIGS. 1-3. When a burst gate pulse is applied to thelatch circuit used as the burst gate circuit 29 at an intermediateinstant in the color burst signal period included in the horizontalblanking interval of the color difference signal, the burst gate circuit29 continues to output the color phase data latched at the intermediateinstant, namely, the data indicating the phase θ' of the color burstsignal which is present in the horizontal blanking interval in the colordifference signal until the next burst gate pulse is applied to theburst gate circuit 29.

The data indicating the phase θ' of the color burst signal outputtedfrom the burst gate circuit 29 is fed to the subtracter 30 as adividend. In this subtracter 30, a predetermined angle (which is 180degrees in these embodiments) is subtracted from this data such that anoperation can be simply effected by using a small numerical value in thesubsequent signal processing circuit.

Further, the data indicating the phase θ' of the color burst signaloutputted from the subtracter 30 is supplied to the subtracters 31 and33 as a dividend.

The portion composed of the subtracters 31 and 33, the feedback ratiocircuit 32 and the frame memory (or the field memory) 34 functions as aphase deviation detecting circuit for generating digital datarepresenting the phase deviation of the color burst signal, which isconstructed in the form similar to that of the well-known recursive typenoise reducing circuit comprised of the frame memory (or the fieldmemory) 34, the subtracters 31 and 33 and the feedback ratio circuit 32.

Turning to FIGS. 4 and 5, an operation of the phase deviation detectingcircuit will be described hereinbelow. FIG. 4 is a diagram forillustrating data in each portion of the phase deviation detectingcircuit in case where the reproduced color signal is not under theinfluence of the head beat phenomenon. FIG. 5 is a diagram forillustrating data in each portion of the phase deviation detectingcircuit in case where the reproduced color signal is under the influenceof the head beat phenomenon.

Further, FIG. 4 (a) and FIG. 5 (a) show data representing the phase θ'of the color burst signal, which is supplied from the subtracter 30 tothe subtracters 31 and 33, every horizontal scanning period. Further,FIG. 4 (b) and FIG. 5 (a) show digital data indicating the phasedeviation Δθ (hereunder sometimes referred to as the phase deviation)corresponding to the phase deviation of the color burst signal suppliedfrom the subtracter 33 to the subtracter 35 in each horizontal scanningperiod.

The phase deviation Δθ is data indicating the phase of the color burstsignal, from which a noncorrelated information component (namely, anoise) between the successive frames (or fields) is removed, andindicates the residual phase error generated in the color burst signalby the APC operation of the APC circuit every horizontal scanningperiod.

Thus, in the subtracter 35 to which a signal representing the phasedeviation Δθ is supplied as a signal indicating a subtrahend, the phasedeviation Δθ is subtracted from the phase of the color difference signaland that of the color burst signal outputted from the operation circuit22 in each horizontal scanning period. Further, the subtracter outputsto the operation circuits 36 and 37 signals representing digital data(θ-Δθ) and (θ'-Δθ), that is, the color phase data obtained by removingthe residual phase errors from the phases of the color difference signaland the color burst signal by the APC operation of the APC circuitprovided in a pre-stage circuit.

FIGS. 4 (c) and 5 (c) show the digital data (θ'-Δθ) representing thecolor phase of the color burst signal outputted from the subtracter 35.

The operation circuit 36 generates a signal sin (θ-Δθ) in the colordifference signal period and a signal sin (θ'-Δθ) in the color burstsignal period on the basis of the color phase data (θ-Δθ) in the colordifference signal period and (θ'-Δθ) in the color burst signal period,which are supplied thereto, and thereafter supplies color phase data ofsin (θ-Δθ) and color phase data of sin (θ'-Δθ) to the multiplier 38.

Similarly, the operation circuit 37 generates a signal cos (θ-Δθ) in thecolor difference signal period and a signal cos (θ'-Δθ) in the colorburst signal period on the basis of the color phase data (θ-Δθ) in thecolor difference signal period and (θ'-Δθ) in the color burst signalperiod, which are supplied thereto, and thereafter supplies color phasedata of cos (θ-Δθ) and color phase data of cos (θ'-Δθ) to the multiplier39.

As above described, the digital data indicating the color amplitude A issupplied to the multipliers 38 and 39. Thus, the color difference signal(the R-Y signal) obtained by removing the residual phase error from thecolor burst signal by the APC operation of the APC circuit is outputtedfrom the multiplier 38 to the output terminal 40. Further, the colordifference signal (the B-Y signal) obtained by removing the residualphase error from the color burst signal by the APC operation of the APCcircuit is outputted from the multiplier 39 to the output terminal 41.

FIG. 6 is a graph for showing the input/output characteristic of thefeedback ratio circuit 32 provided in the phase deviation quantity datagenerating circuit. In this graph, the input/output characteristic ofthe circuit 32 in case where the feed back ratio thereof is 100% isindicated by a dashed line, which is inclined at 45 degrees to thehorizontal axis (the x axis) of the graph, for reference.

In the phase deviation detecting circuit, the data of the successiveframes (or fields) are highly correlated. Therefore, a high feedbackratio, for instance, 90% (indicated by a solid line in FIG. 6) or so maybe employed as the feedback ratio of the circuit 32.

Turning now to FIGS. 11-15, there are shown other color signal circuitsembodying the present invention. Further, in FIGS. 11-15, like referencecharacters denote like or corresponding portions shown in FIGS. 1-3.Thus, the detailed descriptions of the construction and operation ofsuch like or corresponding portions will be omitted for simplicity ofdescription. Incidentally, similarly as in cases of the embodiments ofFIGS. 1-3, there can be used a generating circuit, which has the sameconstruction as the circuit of FIG. 7 has, for generating datarepresenting color amplitude A and data representing color phase θaccording to the present invention other than the circuits of FIGS. 1-3.In the embodiments of FIGS. 11-15, a portion composed of the subtracters31 and 33, the feedback ratio circuit 32 and the frame memory (or thefield memory) 34 generates a difference signal data corresponding to thedifference of the phase θ' of a current color burst signal obtained by aburst gate circuit 29, from the average of the phases of the past colorburst signals and supplies the difference signal data to a nonlinearsignal processing circuit 63. Further, in FIG. 16 which shows theinput/output characteristic of a feedback ratio circuit 32, thehorizontal axis (the x axis) of the graph indicates a frame differenceinput; and the vertical axis (the y axis) an output of the circuit 32.Moreover, similarly as in FIG. 6, the input/output characteristic of thecircuit 32 in case where the feed back ratio thereof is 100% isindicated by a dashed line, which is inclined at 45 degrees to thehorizontal axis, for reference. Furthermore, in the phase deviationdetecting circuit of these embodiments, the data of the successiveframes (or fields) are highly correlated, so that a high feedback ratio,for instance, 90% (indicated by a solid line in FIG. 16) or so may beemployed as the feedback ratio of the circuit 32.

The above described nonlinear signal processing circuit 63 generates anoutput signal, of which the signal level nonlinearly varies according tothe magnitude of the difference signal data inputted thereto, andfurther supplies the output signal to the subtracter 62 as a signalrepresenting a subtrahend.

In case where a circuit having the input/output characteristic as shownin FIG. 17 (namely, a circuit adapted to output 0 when the framedifference input is within the range from -P₂ to +P₁, and output datanearly equal to the frame difference input when the frame differenceinput is within the range from -180 degrees to -P₂ or within the rangefrom +P₁ to 180 degrees) is employed as the nonlinear signal processingcircuit 63 of the embodiment of FIG. 11, the phase of the signal at eachportion of the embodiment of FIG. 11 becomes as illustrated in FIG. 21.

FIG. 21 (a) illustrates how the phase θ' of the current color burstsignal outputted from the burst gate circuit 29 of FIG. 11 changes withtime. Further, FIG. 21 (b) illustrates how the average of the phases ofthe past color burst signals varies with time. Moreover, FIG. 21 (c)illustrates how the output of the subtracter 31 (that is, the phaseobtained by subtracting the average of the phases of the past colorsignals, which is outputted from the frame memory 34, from the phase θ'of the current color signal, which is outputted from the burst gatecircuit 29) varies with time.

If the phase data of FIG. 21 (c) (namely, the data indicating the framedifference data of the phase of the color burst signal) is inputted tothe nonlinear signal processing circuit 63 having the input/outputcharacteristic as shown in FIG. 17, a signal representing the phase dataas shown in FIG. 21 (d) is outputted from the circuit 63 to thesubtracter 62 as a signal representing a subtrahend.

On the other hand, the color phase signal including the color burstsignal having the phase as shown in FIG. 21 (a) is inputted as a signalrepresenting a minuend to the subtracter 62, whereupon the subtrahend asshown in FIG. 21 (d) is thus subtracted from the minuend as shown inFIG. 21 (a). Thereafter, data representing the phase changing as shownin FIG. 21 (e) is outputted from the subtracter 62 to the operationcircuits 36 and 37.

As is apparent from the comparison of the phase shown in FIG. 21 (a) andobtained by using a color signal circuit, which is not according to thepresent invention, with that shown in FIG. 21 (a) and obtained by usingthe color signal circuit of the present invention, can be easilyobtained a color signal, by the use of which the color flicker asoccurring in the prior art is substantially reduced, in case of usingthe color signal circuit of the present invention.

Incidentally, as the nonlinear signal processing circuit 63, anothercircuit having a desirable characteristic may be employed. For example,may be employed a circuit having the input/output characteristic asshown in FIG. 18 (namely, a circuit adapted to gradually increases theoutput level thereof as the frame difference input increases from -P₂ to+P₁, and output data nearly equal to the frame difference input to thesubtracter 62 when the frame difference input is within the range from-180 degrees to -P₂ or within the range from +P₁ to 180 degrees).

Next, in the embodiment of FIG. 12, a component comprised of an absolutevalue circuit 57, a comparator 58, a D-type flip-flop 59 and a switch 60is employed as the nonlinear signal processing circuit 63.

In the circuit of FIG. 12, the subtracter 31 of a generating circuit31-34 for generating the difference signal data of the color burstsignal (that is, the data corresponding to the difference of the phaseθ' of the current color burst signal obtained by the burst gate circuit29 from the average of the phases of the past color burst signals)outputs the difference signal data to the absolute value circuit 57 anda fixed contact H of the switch 60.

Further, an output of the absolute value circuit 57 is compared with apresent threshold value α in the comparator 58. If the value of theoutput of the circuit 57 is greater than the threshold value α, a clocksignal is supplied from the comparator 58 to the D-type flip-flop 59.

When the level of the output Q of the flip-flop 59 goes high in responseto the clock signal, the movable contact V of the switch 60 is switchedfrom the fixed contact L to the contact H.

When the contact V of the switch 60 is in touch with the contact L, asignal indicating a subtrahend 0 is fed to the subtracter 62. Incontrast, when the contact V of the switch 60 is in touch with thecontact H, the difference signal data outputted from the subtracter 31is fed to the subtracter 62 as the subtrahend. Therefore, it is apparentthat the circuit 63 of FIG. 12 operates as a nonlinear signal processingcircuit having an input/output characteristic as shown in FIG. 17.

Next, in the embodiment of FIG. 13, a component comprised of an absolutevalue circuit 57, comparators 58 α and 58 β, a D-type flip-flop 59 and aswitch 60 is employed as the nonlinear signal processing circuit 63.

In the circuit of FIG. 13, the subtracter 31 of a generating circuit31-34 for generating the difference signal data of the color burstsignal outputs the difference signal data to the absolute value circuit57 and a fixed contact H of the switch 60.

Further, an output of the absolute value circuit 57 is compared with apreset threshold value α in the comparator 58 α and is also comparedwith another preset threshold value β in the comparator 58 β.Incidentally, the value α is set to be greater than the value β.

If the value of the output of the circuit 57 is greater than thethreshold value α, a clock signal is supplied from the comparator 58 αto the D-type flip-flop 59.

In contrast with this, if the value of the output of the circuit 57 isless than the threshold value β, a clearing signal is supplied from thecomparator 58 β to the D-type flip-flop 59.

When the level of the output Q of the flip-flop 59 goes high in responseto the clock signal, the position of the movable contact V of the switch60 is changed from the fixed contact L to the contact H.

When the contact V of the switch 60 is in touch with the contact L, asignal indicating a subtrahend 0 is fed to the subtracter 62. Incontrast, when the contact V of the switch 60 is in touch with thecontact H, the difference signal data outputted from the subtracter 31is fed to the subtracter 62 as the subtrahend.

Thus, the circuit 63 of FIG. 13 operates as a nonlinear signalprocessing circuit having an input/output characteristic as shown inFIG. 19.

FIG. 22 (a) illustrates how the phase θ' of the current color burstsignal outputted from the burst gate circuit 29 of FIG. 13 changes withtime. Further, FIG. 22 (b) illustrates how the average of the phases ofthe past color burst signals outputted from the frame memory 34 of FIG.13 varies with time. Moreover, FIG. 22 (c) illustrates how the output ofthe subtracter 31 (namely, the phase obtained by subtracting the averageof the phases of the past color signals from the phase θ' of the currentcolor signal outputted from the burst gate circuit 29) varies with time.

If the phase data of FIG. 22 (c) (namely, the data indicating the framedifference data of the phase of the color burst signal) is inputted tothe nonlinear signal processing circuit 63 having the input/outputcharacteristic as shown in FIG. 19, a signal representing the phase dataas shown in FIG. 22 (d) is outputted from the circuit 63 to thesubtracter 62 as a signal representing a subtrahend.

On the other hand, the color phase signal including the color burstsignal having the phase as shown in FIG. 22 (a) is inputted as a signalrepresenting a minuend to the subtracter 62, whereupon the subtrahend asshown in FIG. 22 (d) is thus subtracted from the minuend as shown inFIG. 22 (a). Thereafter, data representing the phase changing as shownin FIG. 22 (e) is outputted from the subtracter 62 to the operationcircuits 36 and 37.

Next, in the embodiment of FIG. 14 which is similar to that of FIG. 13,a component comprised of an absolute value circuit 57, comparators 58 αand 58 β, a D-type flip-flop 59, a switch 60, nonlinear signalprocessing units 61a and 61b is employed as the nonlinear signalprocessing circuit 63. For simplicity of description, only thedifferences between the embodiments of FIGS. 13 and 14 will be describedhereinbelow.

In the circuit of FIG. 14, the subtracter 31 of a generating circuit31-34 for generating the difference signal data of the color burstsignal outputs the difference signal data to the absolute value circuit57, to a fixed contact a of the switch 60 through the unit 61a and to afixed contact b of the switch 60 through the unit 61b.

Further, when the contact V of the switch 60 is in touch with thecontact L, a signal outputted from the unit 61b is fed to the subtracter62 as a signal indicating a subtrahend. In contrast, when the contact Vof the switch 60 is in touch with the contact H, an output signal of theunit 61a is fed to the subtracter 62 as a signal indicating thesubtrahend.

Thus, if devices having the input/output characteristic as shown in FIG.18 are used as the units 61a and 61b, the circuit 63 of FIG. 14 operatesas a nonlinear signal processing circuit having an input/outputcharacteristic as shown in FIG. 23.

Next, referring to FIG. 15, there is shown another color signal circuitembodying the present invention, in which the phase deviation quantityΔθ of the color burst signal obtained as a subtracter 33 (that is, theresidual phase error Δθ included in the color signal by the APCoperation of the APC circuit provided in the pre-stage circuit) issubtracted from the color phase signal.

This color signal circuit of FIG. 15 is different in construction fromthe color signal circuit of FIG. 11 in that an output of a subtracter 62is fed to a subtracter 35 as a minuend and further an output of thesubtracter 33 is also fed to the subtracter as a subtrahend and that anoutput of the subtracter 35 is supplied to operation circuits 36 and 37.Thereby, the color signal circuit of FIG. 15 has an advantage in thatthe residual phase error Δθ generated by the APC operation of the APCcircuit and included in a reproduced color signal can be removed andthat the correction of the hue can be preferably performed.

Further, in the color signal circuit of FIG. 15, a portion composed ofthe subtracters 31 and 33, a feed back ratio circuit 32 and a framememory (or a field memory) 34 operates as follows. Namely, (1)difference signal data corresponding to the difference of the phase θ'of a current color burst signal obtained by a burst gate circuit 29 fromthe average of the phases of past color signals is supplied from thesubtracter 31 to a nonlinear signal processing circuit 63, and (2) datarepresenting the phase deviation quantity Δθ of the color burst signalis supplied from the subtracter 33 to the subtracter 35. Incidentally, acircuit having an input/output characteristic as shown in, for example,FIG. 16 is used as the feedback ratio circuit 32.

Further, the nonlinear signal processing circuit 63 generates an outputsignal, of which the signal level nonlinearly varies according to themagnitude of the difference signal data inputted thereto, and furthersupplies the output signal to the subtracter 62 as a signal representinga subtrahend.

In case where a circuit having the input/output characteristic as shownin FIG. 17 (namely, a circuit adapted to output 0 when the framedifference input is within the range from -P₂ to +P₁, and output datanearly equal to the frame difference input when the frame differenceinput is within the range from -180 degrees to -P₂ or within the rangefrom +P₁ to 180 degrees) is employed as the nonlinear signal processingcircuit 63 of the embodiment of FIG. 15, the phase of the signal at eachportion of the embodiment of FIG. 15 becomes as illustrated in FIGS. 23and 24.

FIG. 23 (a) illustrates how the phase θ' of the current color burstsignal outputted from the burst gate circuit 29 of FIG. 15 changes withtime. Further, FIG. 23 (b) illustrates how the average of the phases ofthe past color burst signals varies with time. Moreover, FIG. 23 (c)illustrates how the output of the subtracter 31 (that is, the phaseobtained by subtracting the average of the phases of the past colorsignals, which is outputted from the frame memory 34, from the phase θ'of the current color signal, which is outputted from the burst gatecircuit 29) varies with time.

If the phase data of FIG. 23 (c) (namely, the data indicating the framedifference data of the phase of the color burst signal) is inputted tothe nonlinear signal processing circuit 63 having the input/outputcharacteristic as shown in FIG. 17, a signal representing the phase dataas shown in FIG. 23 (d) is outputted from the circuit 63 to thesubtracter 62 as a signal representing a subtrahend.

On the other hand, the color phase signal including the color burstsignal having the phase as shown in FIG. 23 (a) is inputted as a signalrepresenting a minuend to the subtracter 62, whereupon the subtrahend asshown in FIG. 23 (d) is thus subtracted from the minuend as shown inFIG. 23 (a). Thereafter, data representing the phase changing as shownin FIG. 24 (a) is outputted from the subtracter 62 to the subtracter 35.Incidentally, the digital data representing the phase deviation quantityΔθ of the color burst signal in each horizontal scanning period as shownin FIG. 24 (b) is outputted from the subtracter 33 to the subtracter 35.Further, in the subtracter 35, the data indicating the phase deviationquantity Δθ is subtracted from the data outputted from the subtracter62. Then, the subtracter 35 outputs digital data representing the colorphase, from which the residual phase error included in the colordifference signal and in the color burst signal by the APC operation ofthe APC circuit provided in the pre-stage circuit is removed, as shownin FIG. 24 (c) to the operation circuits 36 and 37.

Further, the operation circuit 36 supplies the color phase data obtainedby effecting an operation on the basis of the digital data representingthe color phase supplied thereto to a multiplier 38. On the other hand,the operation circuit 37 supplies the color phase data obtained byeffecting an operation on the basis of the digital data representing thecolor phase supplied thereto to a multiplier 39.

As shown in FIG. 15, the digital data representing the color amplitude Ais fed to the multipliers 38 and 39. Thus, a color difference signal (anR-Y signal), from which the residual phase error is removed, isoutputted from the multiplier 38 to an output terminal 40. On the otherhand, another color difference signal (an B-Y signal), from which theresidual phase error is removed, is outputted from the multiplier 39 toan output terminal 41.

As described above, in the color signal circuits of FIGS. 1-3 and 11-15,a circuit having a high feedback ratio is employed as the feedback ratiocircuit 32 in order to have sufficient effects thereof. Therefore, incase where an object to be processed by the color signal circuit isswitched from a color signal sent form a current signal source to acolor signal sent from another new signal source and further the phaseof the color signal from the new signal source is largely different fromthat of the color burst signal corresponding to the color signalsupplied from the current signal source to the color signal circuit, ittakes relatively long time till the reproduced image returns to normalcondition. Namely, the portion 31-34 for generating the differencesignal data corresponding to the difference of the phase θ' of thecurrent color burst signal obtained by the burst gate circuit 29 fromthe average of the past color burst signals generates the differencesignal data in such a manner to obtain what is called flywheel effectsin response to the input color burst signal. Thus, in case where theobject to be processed by the color signal circuit is switched from thecolor signal sent form the previous signal source to the color signalsent from the new signal source and further the phase of the colorsignal from the new signal source is largely different from that of thecolor burst signal corresponding to the color signal supplied from theprevious signal source to the color signal circuit, it takes long timetill the difference between the phase of the current color burst signaland the average of the phases of the color burst signals becomessufficiently small. Therefore, the phase of the color signal, which isto be corrected on the basis of the signal generated in the color signalprocessing circuit, is largely deviated over long time. Thus, as abovedescribed, it takes relatively long time till the reproduced imagereturns to normal condition. The present invention is accomplished toresolve this problem.

Turning now to FIGS. 25 and 28, there are shown other color signalcircuits embodying the present invention devised to resolve the problemas immediately above described. Further, referring to FIGS. 26 and 27,there are shown control circuits which are different in constructionfrom each other. Incidentally, in FIGS. 25-28, like reference charactersdenote like or corresponding portions shown in FIGS. 1 and 11. Thus, thedetailed descriptions of the construction and operation of such like orcorresponding portions will be omitted for simplicity of description.Furthermore, similarly as in cases of the embodiments of FIGS. 1-3 and11-15, there can be used a generating circuit, which has the sameconstruction as the circuit of FIG. 7 has, for generating datarepresenting color amplitude A and data representing color phase θaccording to the present invention other than the circuits of FIGS. 25and 28. Thus, the description of the construction and operation of thegenerating circuit will be also omitted.

FIG. 25 shows the construction of the color signal circuit similar tothat of the color signal circuit of FIG. 11. However, in this circuit ofFIG. 25, the output data of a subtracter 31 is fed to a control circuit201 and the feed back ratio of a feedback ratio circuit 32 is changed inaccordance with the control signal generated by the control circuit 201.Further, FIG. 28 shows the construction of the color signal circuitsimilar to that of the color signal circuit of FIG. 1. However, in thecircuit of FIG. 28, the output data of a subtracter 31 is fed to acontrol circuit 201 and the feed back ratio of a feedback ratio circuit32 is changed in accordance with the control signal generated by thecontrol circuit 201.

Further, in the color signal circuit of FIG. 25, difference signal datacorresponding to the difference of the phase θ' of a current color burstsignal obtained by a burst gate circuit 29 from the average of thephases of past color signals is supplied from the subtracter 31 to anonlinear signal processing circuit 63. Moreover, in the circuit of FIG.28, data representing the phase deviation Δθ of the color burst signalis supplied from the subtracter 33 to a subtracter 35 as a subtrahend.

However, in the color signal circuits of FIGS. 25 and 28, the feedbackratio of the feedback ratio circuit 32 is controlled in accordance witha control signal supplied from an output terminal b of the controlcircuit 201 to the circuit 32.

Furthermore, the control circuit 201 is provided with a first countingunit for counting the number of data, which are supplied from thesubtracter 31 to an input terminal a thereof (that is, data representthe difference of the data indicated by a color phase signal andobtained on the basis of a current color synchronizing signal from theaverage of past color signals) and are equal to or greater than apredetermined value of the difference, every vertical scanning period.When the number of the vertical scanning periods, in each of which thenumber counted by the first counting unit exceeds a predeterminednumber, is in excess of another predetermined number, the controlcircuit 201 generates a control signal and outputs the control signalfrom the output terminal b to the feedback ratio circuit 32, therebyreducing the feedback ratio of the circuit 32. Thus, the control circuit201 is constructed such that it can control the feedback ratio of thefeedback ratio circuit 32.

FIGS. 26 and 27 shows examples of such a control circuit 201. In thecontrol circuit 201 of FIG. 26, the absolute value of the output datasupplied from the subtracter 31 to the input terminal a is firstobtained by the absolute value circuit 202. Then, the thus obtainedabsolute value data is fed from the circuit 202 to a comparator 203,whereupon the data supplied from the circuit 202 is compared with apreset reference value α.

If the data supplied from the circuit 202 is greater than the referencevalue α, the comparator 203 outputs a trigger signal to a monostablemultivibrator 204.

Thereafter, pulses generated by the monostable multivibrator 204 inresponse to the trigger signals are counted by a counter 205.Subsequently, the count obtained by the counter 205 is supplied to acomparator 206. Incidentally, the counter 205 is reset by a signal VDhaving a vertical scanning period, so that the value of the count sentfrom the counter 205 to the comparator 206 is a value obtained everyvertical scanning period.

Then, in the comparator 206, the value of the count supplied from thecounter 205 thereto is compared with a preset reference value β. If thevalue of the count is greater than the reference value β, the comparator206 outputs a signal, of which the level is high, to a monostablemultivibrator 207 as a trigger signal and to a monostable multivibrator209 through an inverter 208 as a trigger signal.

Further, pulses outputted from the monostable multivibrator 207 are fedto a counter 210 as pulses to be counted. Moreover, pulses outputtedfrom the monostable multivibrator 209 are fed to the counter 210 as areset signal.

Thus, the value of the count held in the counter 210 corresponds to thenumber of the vertical scanning periods in which pulses outputted fromthe monostable multivibrator 207 are successively supplied to thecounter 210.

Thereafter, data indicating the value of the count is outputted from thecounter 210 to a comparator 211, whereupon the value of the count iscompared with a reference value γ preliminarily set therein. If thevalue of the count supplied from the counter 210 is greater than thereference value γ, the comparator 211 outputs to the output terminal b asignal of which the level is high.

Thus, as above described, the control circuit 201 of FIG. 26 can outputthe control signal from the output terminal b thereof when the number ofthe successive vertical scanning periods, in each of which the number ofdata supplied from the subtracter 31 to the input terminal a thereof(that is, data represent the difference of the data indicated by thecolor phase signal and obtained on the basis of the current colorsynchronizing signal from the average of past color signals) greaterthan a predetermined value of the difference exceeds a predeterminednumber, is in excess of another predetermined number.

Next, in the control circuit 201 of FIG. 27, the absolute value of theoutput data supplied from the subtracter 31 to the input terminal a isfirst obtained by the absolute value circuit 202. Then, the thusobtained absolute value data is fed from the circuit 202 to a comparator203, whereupon the data supplied from the circuit 202 is compared with apreset reference value α.

If the data supplied from the circuit 202 is greater than the referencevalue α, the comparator 203 outputs a trigger signal to a monostablemultivibrator 204.

Then, pulses generated in the monostable multivibrator 204 are convertedby a serial-parallel converter 212 into parallel data. Theserial-parallel converter 212 outputs n-digit output data (n is apredetermined natural number) to an AND circuit 213. Further, theconverter 212 is reset by the signal VD having a period equal to thevertical scanning period. Thus, when pulses, of which the number isequal to or greater than n, are outputted from the monostablemultivibrator 204 in a vertical scanning period, the AND circuit 213outputs a signal, of which the level is high, to a data input terminalof a serial-parallel converter 215. Further, an output of the ANDcircuit 213 is fed to a reset terminal of the converter 215 through aninverter 214.

The converter 215 receives an output of the AND circuit 213 as data ifthe level of the output of the AND circuit 213 is high and is reset ifthe level of the output of the AND circuit 213 is low. Therefore, anoutput of an AND circuit 216, to which m-digit data outputted from theconverter 215 is supplied (m is a predetermined natural number), is sentto the output terminal b in case where when pulses, of which the numberis equal to or more than n, are outputted from the monostablemultivibrator 204 in each of the successive m vertical scanning periods,that is, in case where the number of data supplied from the subtracter31 to the input terminal a thereof (that is, data represent thedifference of the data indicated by the color phase signal and obtainedon the basis of the current color synchronizing signal from the averageof past color signals) greater than a predetermined value of thedifference exceeds a predetermined number, is in excess of anotherpredetermined number.

As above described, the signal, of which the level is high, outputtedfrom the output terminal b changes the ratio of the feedback ratio ofthe circuit 32 into 0 (or a small value) and causes the portion 31-34 tochange the value indicated by the difference signal outputted from thesubtracter 31 thereof into a small value in a short period of time.

Thus, in case where an object to be processed by the color signalcircuit is switched from a color signal sent form a current signalsource to a color signal sent from another new signal source and furtherthe phase of the color signal from the new signal source is largelydifferent from that of the color burst signal corresponding to the colorsignal supplied from the current signal source to the color signalcircuit, the feedback ratio of the feedback circuit 32 is changed into 0(or a small value) in accordance with the control signal outputted bythe control circuit 201 and further the data supplied from the portion31-34 to the nonlinear signal processing circuit 63 (in case of theembodiment of FIG. 25) or the subtracter 35 (in case of the embodimentof FIG. 28) is also changed into 0 (or another small value). Further, acolor phase signal issued from a subtracter 62 of the embodiment of FIG.25 to the subsequent circuit and a color signal issued from thesubtracter 35 to the subsequent circuit make the color phase signals ofthe color signals supplied from the new signal source to the colorsignal circuit. Thereby, the defect of the color signal circuits ofFIGS. 1-3 and 11-15 can be eliminated.

Next, turning to FIG. 31, there is shown still another color signalcircuit bodying the present invention. Incidentally, in FIG. 31, likereference characters denote like or corresponding portions shown inFIGS. 1-3. Thus, the detailed descriptions of the construction andoperation of such like or corresponding portions will be omitted forsimplicity of description. Incidentally, in FIG. 31, reference numeral16 designates a coefficient generating circuit, which will be describedlater.

Further, in the circuit of FIG. 31, an operation circuit 22 outputs dataindicating a color phase θ directly to operation circuits 36 and 37.

Moreover, data indicating the value of 2A outputted from an adder 27 ismultiplied by 1/2 by an operation circuit 8. Then, data representingcolor amplitude A is supplied from the circuit 28 to a multiplier 35 anda burst gate circuit.

Furthermore, the circuit 22 can output data representing the amplitudeof the color burst signal corresponding to a specific portion of eachhorizontal blanking interval of color difference signals supplied toinput terminals 19 and 20. Moreover, similarly as in cases of theembodiments of FIGS. 1-3 and 11-15, there is a generating circuit, whichhas the same construction as the circuit of FIG. 7 has, for generatingdata representing color amplitude A and data representing color phase θaccording to the present invention other than the circuit of FIG. 31.Further, the description of the construction and operation of thegenerating circuit will be also omitted for simplicity of description.Moreover, data outputted from the circuit 22, which obtains data at anintermediate instant of a color burst signal period in the horizontalblanking interval of the color difference signal, is data representingthe amplitude of the color burst signal.

Further, for instance, a latch circuit may be used as the burst gatecircuit 29, to which is the color phase data is supplied, in theembodiments of FIGS. 1-3. When a burst gate pulse is applied to thelatch circuit used as the burst gate circuit 29 at an intermediateinstant in the color burst signal period included in the horizontalblanking interval of the color difference signal, the burst gate circuit29 continues to output the color phase data latched at the intermediateinstant, namely, the data indicating the amplitude A of the color burstsignal which is present in the horizontal blanking interval in the colordifference signal until the next burst gate pulse is applied to theburst gate circuit 29.

The data indicating the amplitude A of the color burst signal outputtedfrom the burst gate circuit 29 is fed to subtracters 31 and 33 as adividend.

The portion composed of the subtracters 31 and 33, the feedback ratiocircuit 32 and the frame memory (or the field memory) 34 is a well-knownrecursive type noise reducing circuit (hereunder sometimes referred toas a noise reducer) comprised of the frame memory (or the field memory)34, the subtracters 31 and 33 and the feedback ratio circuit 32.

Further, the feedback ratio circuit 32 of the noise reducer has aninput/output characteristic as shown in FIG. 16. Furthermore, in thenoise reducer for reducing noises in the color burst signal, the data ofthe successive frames (or fields) are highly correlated, so that a highfeedback ratio, for instance, 90% (indicated by a solid line in FIG. 16)or so may be employed as the feedback ratio of the circuit 32.

By the above described noise reducer, the noise is removed from orreduced in the color burst signal. After the noise is reduced, the colorburst signal is supplied to the coefficient generating circuit 16adapted to generate a coefficient such that a predetermined constantvalue of the amplitude can be obtained by multiplying the value of theamplitude of the color burst signal by the coefficient. The coefficientgenerating circuit can be constructed by using a translation table.

Thus generated coefficient corresponding to the amplitude of the colorburst signal, from which the noise is removed, is supplied from thecircuit 16 to a multiplier 35.

Further, the color amplitude signal outputted from an operation circuit28 is also supplied to the multiplier 35. Thus, the color amplitudesignal, of which the amplitude is modified or corrected, is outputtedfrom the multiplier 35 to the multipliers 38 and 39.

Further, the data indicating sin θ is outputted from an operationcircuit 36 to the multipliers 38 and 39. Moreover, the data indicatingcos θ is supplied to the multiplier 39. Thus, a color difference signal(an R-Y signal), of which the signal level is constant, is outputtedfrom the multiplier 38 to an output terminal 40. Further, another colordifference signal (a B-Y signal), of which the signal level is constant,is outputted from the multiplier 39 to an output terminal 41.

FIG. 32 is a diagram for illustrating an operation of the color signalcircuit of FIG. 31. In this figure, reference character A□ denotes apreset value of the final output amplitude of the ACC (Automatic Chromalevel Control) circuit.

FIG. 32 (a) shows the data indicating the amplitude A of the color burstsignal, which is fed from the burst gate circuit 29 to the subtracters31 and 33, in each horizontal scanning period. Further, FIG. 32 (b)shows data indicating the average of the amplitude of the past colorburst signals fed from the frame memory (or field memory) 34 to thesubtracter 31. Moreover, FIG. 32 (c) shows data indicating the framedifference of the amplitude of the color burst signal outputted from thesubtracter 31 in each horizontal scanning period.

Furthermore, FIG. 32 (d) shows data outputted from the feedback ratiocircuit 32. FIG. 32 (e) digital data representing the color amplitude ofthe color burst signal, which noises are reduced in and removed from,outputted from the feedback ratio circuit 32.

Further, FIG. 32 (f) shows the coefficient generated by the coefficientgenerating circuit 16 to which digital data indicating the coloramplitude of the color burst signal of FIG. 32 (e). Moreover, FIG. 32(g) shows data outputted from the multiplier 35 and obtained bymultiplying the data indicating the variable color amplitude, which isfed from the operation circuit 28 to the multiplier 35, by thecoefficient generated by the coefficient generating circuit 16 of FIG.33 (f).

Next, referring now to FIGS. 33-35, there are other color signalcircuits embodying the present invention. Incidentally, in FIGS. 33-35,like reference characters denote like or corresponding portions shown inFIGS. 1-3. Thus, the detailed descriptions of the construction andoperation of such like or corresponding portions will be omitted forsimplicity of description. Incidentally, in FIG. 31, reference numeral11 designates an adder, to which data representing the color phase θ isoutputted from an operation circuit 22 and further phase data to be usedfor shifting a phase is also supplied.

Further, similarly as in cases of the embodiments of FIGS. 1-3, 11-15and 25 and 28, there can be used a generating circuit, which has thesame construction as the circuit of FIG. 7 has, for generating datarepresenting color amplitude A and data representing color phase θaccording to the present invention other than the circuits of FIGS. 33and 35.

In cases of the embodiments of FIGS. 33-35, the phase data for shiftingthe phase is added to the color phase data outputted by the circuit 22by the adder 11, so that the phase data of the color phase signaloutputted from the circuit 11 is different from the color phase dataoutputted by the circuit 22 and changes according to the phase data,which is supplied to the adder 11, for shifting the phase. Thus, the huecontrol is effected by changing a preset value of the phase data forshifting the phase.

A color phase signal outputted from the adder 11 (that is, the colorsignal of which the phase is shifted by the adder 11 by the phase datasupplied thereto for shifting the phase) is supplied to an operationcircuit 36, whereupon a signal indicating sin θ is produced. Further,the signal indicating sin θ is sent to a multiplier 38, whereupon thedata representing sin θ is multiplied by data indicated by the coloramplitude signal A. Finally, the R-Y signal indicating Asin θ isoutputted from the multiplier 38 to an output terminal 40.

Further, the color phase signal outputted from the adder 11 (that is,the color signal of which the phase is shifted by the adder 11 by thephase data supplied thereto for shifting the phase) is supplied to anoperation circuit 37, whereupon a signal indicating cos θ is produced.Then, the signal indicating cos θ is sent to a multiplier 39, whereuponthe data representing cos θ is multiplied by data indicated by the coloramplitude signal A. Finally, the B-Y signal indicating Asin θ isoutputted from the multiplier 39 to another output terminal 41.

Thus, as is apparent from the foregoing description, the hue of the A-Ysignal outputted to the output terminal 40 and that of the B-Y signaloutputted to the output terminal 41 are changed by the phase data forshifting the phase.

While the preferred embodiments of the present invention have beendescribed above, it is to be understood that the present invention isnot limited thereto and that other modifications will be apparent tothose skilled in the art without departing from the spirit of theinvention. The scope of the present invention, therefore, is to bedetermined solely by the appended claims.

What is claimed is:
 1. A color signal processing circuit comprising:asignal conversion means for converting two color difference signals,which are equivalent to two color difference signals to be obtained byperforming color demodulation of a color signal by using two colordifference axes intersecting perpendicularly to each other, into a coloramplitude signal corresponding to the amplitude of the color signal anda color phase signal corresponding to a phase of the color signal; adifference signal generating means for generating in response to a colorsynchronizing signal a difference signal representing the differencebetween a current color signal outputted by said signal conversion meansand the average of past color phase signals; a nonlinear signalprocessing means for nonlinearly changing an output thereof depending onthe magnitude of the difference signal generated by said differencesignal generating means and the current color phase signal; a signalmodification means for generating and outputting a modified color phasesignal which represents data to be obtained by subtracting a valueindicated by the output signal of said nonlinear processing means from avalue indicated by the current color phase signal outputted from saidsignal conversion means; and a color difference signal generating meansfor generating two color difference signals on the basis of the coloramplitude signal and the modified color phase signal outputted from saidsignal modification means.
 2. A color signal processing circuitcomprising:a signal conversion means for converting two color differencesignals, which are equivalent to two color difference signals to beobtained by performing color demodulation of a color signal by using twocolor difference axes intersecting perpendicularly to each other, into acolor amplitude signal corresponding to the amplitude of the colorsignal and a color phase signal corresponding to the phase of the colorsignal; a difference signal generating means for generating in responseto a color synchronizing signal a difference signal representing thedifference between a current color signal outputted by said signalconversion means and the average of the past color phase signals; anonlinear signal processing means for nonlinearly changing an outputthereof depending on the magnitude of the difference signal generated bythe difference signal generating means and the current color phasesignal; a first signal modification means for generating and outputtinga first modified color phase signal which represent data obtained bysubtracting a value indicated by the output signal of said nonlinearprocessing means from a value indicated by a current color phase signaloutputted from said signal conversion means; a phase-deviation-quantitysignal generating means for generating a phase deviation signalcorresponding to a phase deviation quantity of the color phase signaloutputted from said conversion means; a second signal modification meansfor generating and outputting a second modified color phase signal whichrepresents data to be obtained by subtracting data indicated by thephase deviation quantity signal, which is outputted from saidphase-deviation-quantity signal generating means, from data indicated bythe first modified color phase signal outputted from said first modifiedsignal modification means; and a color difference signal generatingmeans for generating two color difference signals on the basis of thecolor amplitude signal and the second modified color phase signaloutputted from said second signal modification means.
 3. A color signalprocessing circuit comprising:an average-value-signal generating meansfor generating and outputting an average-value-signal which representsan average or mean of values indicated by past color phase signals, theaverage being obtained by supplying data indicated by the color phasesignal, which corresponds to a phase of a color signal obtained on thebasis of two color difference signals having a signal form similar totwo color difference signals to be obtained by effecting colordemodulation of a color signal by using two color difference axesintersecting perpendicularly to each other, during a period of a colorsynchronizing signal sent a recursive type digital filter which includesa memory capable of storing a signal having a period obtained bymultiplying a vertical scanning period by an integer, said digitalfilter further including an arithmetic circuit and a feedback ratiocircuit having a high feedback ratio; a count-signal generating meansfor generating and outputting, during every vertical scanning period, acount signal representing a number of data indicated by the color phasesignal on the basis of a current color synchronizing signal, from whichthe average value indicated by the average-value-signal is subtracted toobtain a difference equal to or larger than a predetermined value; and afeedback-ratio-control-signal generating means for generating a controlsignal to reduce the feedback ratio of the feedback ratio circuit when anumber of vertical scanning periods, in which the number of dataindicated by the count signal is in excess of a predetermined value,exceeds a predetermined value.
 4. A color signal processing circuitcomprising:an average-value-signal generating means for generating andoutputting an average-value-signal which represents an average or meanof values indicated by past color phase signals, the average beingobtained by supplying data indicated by the color phase signal, whichcorresponds to a phase of the color signal obtained on the basis of twocolor difference signals having a signal form similar to two colordifference signals to be obtained by effecting the color demodulation ofa color signal by using two color differences axes intersectingperpendicularly to each other, during a period of a color synchronizingsignal sent to a recursive type digital filter which includes a memorycapable of storing a signal having a period obtained by multiplying avertical scanning period by an integer, said digital filter furtherincluding an arithmetic circuit and a feedback ratio circuit having ahigh feedback ratio; a count-signal generating means for generating andoutputting, during every vertical scanning period, a count signalrepresenting a number of data indicated by the color phase signal on thebasis of a current color synchronizing signal, from which the averagevalue indicated by the average-value-signal is subtracted to obtain adifference equal to or larger than a predetermined value; afeedback-ratio-control-signal generating means for generating a controlsignal to reduce the feedback ratio of the feedback ratio circuit when anumber of vertical scanning periods, in which the number of dataindicated by the count signal is in excess of a predetermined value,exceeds a predetermined value; and a phase-deviation-quantity signalgenerating means for generating a phase deviation quantity signalcorresponding to a quantity of a phase deviation of a color phase signaloutputted from the digital filter.
 5. A color signal processing circuitcomprising:a signal conversion means for converting two color differencesignals, which are equivalent to two color difference signals to beobtained by performing color demodulation of a color signal by using twocolor difference axes intersecting perpendicularly to each other, into acolor amplitude signal corresponding to an amplitude of the color signaland a color phase signal corresponding to a phase of the color signal; anoise reducing means for reducing noises in the color amplitude signalobtained correspondingly to a color synchronizing signal and foroutputting the color amplitude signal, the noise in which is reduced; acoefficient-signal generating means for generating a signal representinga coefficient such that when the amplitude of the color amplitude signaloutputted from the noise reducing means is multiplied by thecoefficient, a predetermined constant value of the amplitude isobtained; a product-signal generating means for generating a signalrepresenting a product obtained by multiplying the color amplitudesignal fed from said noise reducing means by the coefficient fed fromsaid coefficient-signal generating means; a color amplitude signalsupplying means for supplying the color amplitude signal outputted fromsaid signal conversion means to said product-signal generating means;and a color difference signal generating means for generating apredetermined color difference signal on the basis of the coloramplitude signal outputted from said product-signal generating means andthe color phase signal outputted from said signal conversion means.
 6. Acolor signal processing circuit comprising:signal conversion means forconverting two color difference signals, which are equivalent to twocolor difference signals to be obtained by performing color demodulationof a color signal by using two color difference axes intersectingperpendicularly to each other, into a color amplitude signalcorresponding to an amplitude of the color signal and a color phasesignal corresponding to a phase of the color signal; a signalmodification means for generating and outputting a modified color phasesignal which represents data to be obtained by adding phase shiftingdata to or subtracting the phase shifting data from data indicated bythe color phase signal outputted from said signal conversion means; anda color signal generating means for generating a predetermined colorsignal on the basis of the color amplitude signal and the color phasesignal outputted from said signal modification means.